The present invention relates to an electrodynamic or moving-coil loudspeaker.
Electrodynamic loudspeakers of the type under discussion have been known. For example, DE-A-27 13 023 discloses an electrodynamic loudspeaker with an amplifier for feeding a moving or voice coil. The loudspeaker is constructed as a low-frequency speaker or woofer. The effective output impedance of the amplifier is equivalent to a negative resistance connected in series with an anti-resonant circuit. The negative resistance has substantially the same value as the resistance of the speaker moving coil. Through operating the speaker with such an amplifier, it is possible to modify the bass characteristics of the speaker, which is equivalent to modifying the mechanical parameters of the speaker component, as well as its moving mass, damping and modulation. Thus, in this way the self-resonant frequency of the speaker is controlled and simultaneously another resonant frequency is forced, which is better tuned to the speaker casing.
The disadvantage of this solution is that, although it brings advantages in the case of woofers or on reproducing bass notes by another speaker, it cannot be used for improving medium frequency and high frequency speakers or tweeters, or for improving the reproduction of medium and high frequency notes, because in the case of the latter said problems with the self-resonant frequency either do not occur, or only occur to a very limited extent. In addition, this solution does not provide a foreseeable frequency response indicating a clear tendency and such as is required for other components (e.g. amplifiers, recording equipment, etc.) of an electroacoustic chain. Therefore the speaker remains the poorest component of such a chain, which starts with the microphone and ends with the speaker. In the case of the speaker the linear and nonlinear distortions are much worse than in the other components of such an electroacoustic chain, such as e.g. the microphone, amplifier, mixer, memory, etc. The improvements achieved with the measures according to the aforementioned patent application and other known measures are of such a minor nature that they often do not justify the expenditure.
In the article published in Audio-Engineering, August, 1951, by W. Clements entitled "A new approach to loudspeaker damping", an amplifier circuit with a negative impedance is disclosed, which is designed in such a way that as a result, the impedance of the moving coil of a following speaker almost disappears. The advantage aimed at is that the speaker will be very considerably damped.
Thus, an amplifier circuit of the type described in the above article is in particular intended for use for damping resonances of the speaker at low frequencies. In the case of multipath loudspeakers the resonant frequency is only in the transmission range for woofers. In the case of medium-frequency speakers and tweeters said resonant frequency is outside the transmission range. In the case of multipath systems such an amplifier circuit is consequently exclusively used as a drive for woofers. The frequency response is not improved by such an amplifier circuit in the case of medium-frequency speakers and tweeters, because other means are used for this purpose.